Concrete, Gunite, and Shotcrete: Important Differences Explained
Concrete, Gunite, and Shotcrete. It can be difficult to explain the differences between these words to someone outside of the construction industry. Whether you’re a layperson or a concrete professional who struggles to bridge the educational gaps with your customers, this article should help clear up confusion.
Concrete is a mix of cement, sand, and a coarse aggregate, which is usually stone or gravel, mixed with water. Gunite and shotcrete are names for different results based on the mixing process.
The cement, sand, and aggregate are the initial mixture. The distinction between gunite or shotcrete depends on how and when the builder mixes in the water.
Technically speaking, the term shotcrete refers to either wet- or dry-mix concrete as long as it’s applied using a hose–or “shot” out of the hose. Usually, though, shotcrete is wet mix concrete.
Gunite is concrete applied with the dry-mix process. It remains dry until the user applies water for their needs.
For gunite (dry-mix), the builders load the pre-mixed dry material into the hopper of the delivery equipment.
They use compressed air to send the material to the nozzle, where it mixes with water.
Then it sprays out at super high velocity, which compacts the material on placement.
One of our favorite machines for gunite application is the Airplaco C-10HHdD. This machine is durable and powerful, guaranteeing maximum efficiency for contractors who depend on powerful output to do their jobs.
For shotcrete (wet mix), the builders put the fully mixed wet concrete in equipment hopper and compressed air shoots the material to/through the nozzle.
Again, the material sprays out fast and compresses where applied.
For shotcrete, we love the unique Airplaco Cyclone. It is a particularly useful machine for repair projects.
Pros vs. Cons
-Normally if you’re pouring concrete and you stop and later start back up, those two pours won’t bind together. They’ll be two separate pours. So if you were to stop a rough edge and try to blend the new into the old, it’ll create a cold joint which will look different and most likely crack there.
-When you’re guniting, you can stop and start again without creating that “cold joint” or plane of weakness. Because of the velocity the material is applied, it’ll still bond together.
-Builders have more work time since they mix the cement on-site and can stop and start as needed.
-This process tends to be less expensive than shotcrete.
-The gunite process requires a very skilled operator because that person is in charge of the sand/cement/water ratio. Errors like that can ruin the quality of the concrete.
-The dry mixture could clog the hose pipe.
-Gunite produces a lot of wasteful over-spray, called rebound, that cannot be reused.
-While builders using shotcrete need to be skilled, the concrete is premixed, so there is less technical ability required.
-Shotcrete forms a strong and consistent coating.
-Shotcrete requires less time and can shorten overall project time.
-Since shotcrete is premixed, you have to apply it quickly. You can’t stop and start because it won’t bond.
-Cracks can form from shrinkage if too much water is added to the mix.
-Shotcrete is more expensive than gunite.
-The builders might add water to the cement mixture in the cement truck to keep it from hardening. This can compromise the strength of the concrete.
Hopefully this handy guide will make explaining the difference is concrete mix type a little easier, or, if you were here seeking clarity for yourself, hopefully you’ve now found it. Here at Airplaco, we’ve been industry leaders since 1947, and we take pride in the information we provide. If this article was useful to you, consider getting a quote to see what it would take to add one of our machines to your operation. You’ll find that our helpfulness extends from our blog to our friendly representatives.